In my above-identified related application, I disclose an extruded mounting plate or rack which has locking slots formed in the surface thereof and a cooperating groove formed in a longitudinally extending protrusion or rib in the center of the plate. This protrusion or rib serves as a guide for accurately positioning the frames or mounting brackets of each individual keyboard-actuating implements, such as a solenoid, and the mounting brackets have a pair of laterally extending flanges which are frictionally received in the grooves formed in the central rib. One of the off-set flanges causes spring pressure to be applied to the solenoid which permitted a single screw securement of the solenoid frame to the mounting plate or bar. The present invention eliminates the central rib and grooves and the spring locking tongue but retains the accurate and relatively wide freedom of adjustment of the solenoid frames in a common assembly. According to the present invention, the mounting rack has a longitudinal planar surface, and three screw slots which extend longitudinally along the length of the plate. Two longitudinal actuator alignment ribs are formed integrally on the edges of the planar surface, respectively, one alignment rib being used for aligning every other actuator and the other alignment rib being used for aligning the remaining of the actuators (the alternate ones). In order to achieve a closer packing density with this arrangement, the alternate corners of the actuator mounting brackets which are secured over the center of the locking screws have a cut-out portion so as to permit the frame to be secured by screw fasteners at this central portion of the plate.